Many electrical devices are incorporating touchscreen type displays. A touchscreen is a display that detects the presence, location, and optionally pressure of a touch within the display area, generally by a finger, hand, stylus, or other pointing device. The touchscreen enables a user to interact with the display module directly without requiring any intermediate device, rather than indirectly via a mouse, touchpad or mechanical keyboard arrangement. Touchscreens can be implemented in computers or as terminals to access networks. Touchscreens are commonly found in point-of-sale systems, automated teller machines (ATMs), mobile phones, personal digital assistants (PDAs), portable game consoles, satellite navigation devices, and information appliances.
There are a number of types of touchscreen technologies. A resistive touchscreen panel is composed of several layers including two thin metallic electrically conductive layers separated by thin space. When some object touches the touchscreen panel, the layers are connected at certain point. In response to the object contact, the panel electrically acts similar to two voltage dividers with connected outputs. This causes a change in the electrical current that is registered as a touch event and sent to the controller for processing.
A capacitive touchscreen panel is coated, partially coated, or patterned with a material that conducts a continuous electrical current across a sensor. The sensor exhibits a precisely controlled field of stored electrons in both the horizontal and vertical axes to achieve capacitance. The human body is also an electrical device that has stored electrons and therefore also exhibits capacitance. When a reference capacitance of the sensor is altered by another capacitance field, such as a finger, electronic circuits connected to the panel measure the resultant distortion in the reference capacitance. The measured information related to the touch event is sent to the controller for mathematical processing. Capacitive sensors can either be touched with a bare finger or with a conductive device being held by a bare hand. Capacitive sensors also work based on proximity, and do not have to be directly touched to be triggered. In most cases, direct contact to a conductive metal surface does not occur and the conductive sensor is separated from the user's body by an insulating glass or plastic layer. Devices with capacitive buttons intended to be touched by a finger can often be triggered by quickly waving the palm of the hand close to the surface without touching.
Other types of touchscreen technologies include surface acoustic wave technology that uses ultrasonic waves, infrared touchscreen panels, strain gauge panels coupled to springs, optical imaging, dispersive signal technology, and total internal reflection.
Haptic technology refers to technology which interfaces to the user via the sense of touch by applying forces, vibrations and/or motions to the user. Either the entire device is vibrated, such as the silent mode on a cellular telephone, or only the touch surface is vibrated, such as a haptic touchscreen. Haptic, or tactile, feedback provides confirmation of a button touch or press on a touchscreen control panel, or a confirmation of an action taken.
Haptic feedback is conventionally provided by attaching one or more transducers to the touchscreen, and vibrating the entire, or parts of the, panel using the one or more transducers. In some applications, localized haptic feedback is provided where only the part of the panel actually touched vibrates by using multiple phased actuators and obtaining standing wave patterns on the panel. A transducer converts an electrical signal to mechanical energy. Piezoelectric actuators are sometimes used as the transducers. The piezoelectric actuators vibrate when excited by an electrical signal.
A haptic feedback system includes feedback circuitry coupled to a touch surface, such as a touchscreen, for detecting the location(s) being touched, processing the detecting touch, and providing a haptic feedback to the touch surface in response to the processing. FIG. 1 illustrates a conventional haptic feedback system including a touchscreen 2, a capacitive touchscreen controller 4, a system host controller 8, and a haptic actuator controller. The system host controller 8, the capacitive touchscreen controller 4, and the haptic actuator controller 6 are coupled via a serial bus interface 10. The touchscreen 2 is a capacitive touchscreen having one or more sensors for sensing when the touchscreen is touched. The raw sensed data is transmitted from the sensors to the capacitive touchscreen controller 4. The sensed data is converted by the touchscreen controller 4 to digital information and sent to the system host controller 8 for processing. The system host controller 8 processes the converted sensed data according to what item was selected on the touchscreen 2, as determined by the touched position on the touchscreen 2 and the information displayed on the touchscreen 2 when the touch occurred. For example, a specific application or action to be performed is selected and the system host controller 8 processes that selection. The system host controller 8 decides whether or not to issue a signal to the haptic actuator controller 6 as part of that processing, which in turn signals an actuator of the touchscreen 2. The actuator vibrates the touchscreen. The actuator is any electro-mechanical system that converts electrical energy into mechanical energy. In some applications, the touchscreen 2 can also have one or more force sensing elements for sensing pressure applied to the touchscreen. The pressure data can be used instead of or in addition to the sensed position data to generate the signal provided to the haptic actuator controller 6.
The system host controller 8 introduces latency that delays the haptic response sensed by the user. The system host controller may already be occupied performing other processing tasks, in addition to performing processing tasks associated with the item selected on the touchscreen that initiated the need for haptic response. Sense of touch is very responsive. If the touchscreen is touched, and a vibration (haptic response) is not felt within a relatively short duration, for example 30 milliseconds, the user often concludes that the original touch was not sensed by the touchscreen and another attempt is made, often by pressing harder. Such delays are annoying for the user. The latency of the conventional haptic feedback architecture ranges from a few milliseconds when the system host controller is idle and customized haptic specific software has been added to the operating system of the system host controller to 100 milliseconds or more if the system host controller is busy when the digital information is received. Standard operating systems do not support haptic feedback, such functionality is a customized addition.